Hold Frame in Compositor
You can add a input->image node and open the video file with it.
In the node controls you can set how many frames of your video file you want to use (frames), when to start in your composition (start frame), and the offset value is the one that will allow you to choose the exact frame to be used.
In this example the original quicktime file has 1600 frames but only 1 frame (797) will be displayed, as freeze frame, starting at frame 1 and for the entire length of the composition.